An extraordinary hoard of princely bling, massive pieces of 16th and 17th century silver and gold squirming with ornament and conservatively valued at £10m has been bequeathed to the Ashmolean museum in Oxford by a collector.

One 1608 lapis lazuli and gold bowl alone is valued at "several millions", according to the curator, Professor Tim Wilson, who befriended the dealer Michael Wellby over many years, and persuaded him that the Ashmolean was the perfect home for his treasures after his death.

On the collection's value, Wilson said: "The measure here tends to be 'what would the Prince of Liechtenstein be prepared to pay?' and in this case there's no knowing what lengths he might go to."

Museum director Christopher Brown described the bequest as: "One of the most important acquisitions that has ever been made in the very long history of the Ashmolean museum."

The museum plans to put a few of the most spectacular pieces on display in the next few weeks, but will have to knock down a wall and create a new gallery to display the jaw-dropping assemblage of almost 500 objects together as Wellby intended.

The Ashmolean, which has been on a roll with 900,000 visitors last year, also announced plans for some spectacular exhibitions to celebrate its 330th anniversary this year. They include Old Master drawings by Raphael, Michelangelo and Leonardo da Vinci, a show for which the Chinese artist Xu Bing is making several new works, and a fascinating autumn exhibition improbably pairing Francis Bacon and Henry Moore – contemporary geniuses who, the curators said, had "a wary respect for one another".

However, the revelation of the Wellby bequest inevitably overshadowed the other announcements. Wellby, who died last year, came from a London family of silversmiths and dealers and was an internationally acknowledged expert on northern European Renaissance and baroque silver. His jewellery collection fetched almost £3m at a Sotheby's auction in December, more than three times the estimate. Many of the pieces he kept were cannily acquired in the mid-20th century, when the ornate style described by Wilson as "explosions of panache, craftsmanship and sometimes sheer wackiness" was regarded as old fashioned.

"In the manner of the grand old dealers, he could be quite cagey about where he actually acquired things," Wilson recalled. "There was nothing underhand about it, most were bought at public auctions on the continent, but he liked to play his cards very close to his chest."

Wilson often visited him at home at Haddenham near Oxford, where he recalled "lunching off rather plain china, but sometimes with some splendid silver cups to drink from".

Wellby was fascinated by the nautilus shells, coconuts and ostrich eggs collected by the Tradescant family which became part of the founding collection of the museum. Wilson also showed him around the splendid medieval silver which many Oxford colleges still put out on the high tables for special occasions. Wellby merely remarked: "I enjoyed looking at the goods."

It hadn't been hard to persuade Wellby to bequeath his collection, Wilson said. "Michael believed we would do justice to it, and as far as I am concerned I intend to devote as much as possible of the rest of my career to doing just that."

He already knows that there may be a few dodgy elements in the collection, not outright fakes but pieces that were altered or improved in the 19th century when millionaire collectors such as the Rothschilds were keen on such pieces.

However, the collection undoubtedly has surprises in store even for him. As the conservators were packing up one stupendous silver gilt and enamelled ewer, made in Portugal in around 1510, to show off at the announcement in London, they discovered a mechanism concealed in the base which presumably makes the entire mass of silver and gold rotate.